Recently, efficienies have been realized in the digital transmission of facsimile calls by demodulation and remodulation of the page portion of the call. This enables that portion of the facsimile call to be efficiently transmitted over a digital transmission facility. One such arrangement is disclosed in U.S. patent application of D. O. Anderton and R. L. Daggett Ser. No. 428,560, filed Oct. 30, 1989.
In a prior arrangement, operation of a facsimile page demodulator in a transmitter and a facsimile page remodulator in a receiver is controlled in response to a control message in the facsimile control protocol. In certain facsimile arrangements, particular tone signals are transmitted after the facsimile control protocol message indicating that page data is imminent and before the actual page data arrives. These tone signals are called echo protection tones and are intended to prevent any echo suppressors in the transmission facility from attenuating the facsimile page data. In the prior facsimile demodulation and remodulation transmission arrangement, these tones were not regenerated. Consequently, any echo suppressors in the transmission facility could possibly attenuate the facsimile page data and, thus, corrupt the facsimile transmission. A possible result is that a facsimile machine may fail to receive the facsimile page data. This is extremely undesirable.